[gh-117657] _Py_MergeZeroLocalRefcount isn't loading ob_ref_shared with strong enough semantics (#118111)

DinoV · web-flow · commit b45af00bad34 · 2024-04-19T14:21:01.000-07:00
Use acquire for load of ob_ref_shared
diff --git a/Objects/object.c b/Objects/object.c
@@ -374,7 +374,7 @@ _Py_MergeZeroLocalRefcount(PyObject *op)
     assert(op->ob_ref_local == 0);
 
     _Py_atomic_store_uintptr_relaxed(&op->ob_tid, 0);
-    Py_ssize_t shared = _Py_atomic_load_ssize_relaxed(&op->ob_ref_shared);
+    Py_ssize_t shared = _Py_atomic_load_ssize_acquire(&op->ob_ref_shared);
     if (shared == 0) {
         // Fast-path: shared refcount is zero (including flags)
         _Py_Dealloc(op);
